Anti-Contamination

1.Problems of Contaminated Insulator

When an insulator is polluted and wetted,

• Reduction of withstand voltage causes flashover accidents
• Erosion of glass insulators by increased leakage current
• Electrolytic corrosion in metal fittings => Zinc Sleeve

Erosion

2. Type of Contamination

• Marine Contamination: Sea salt, NaCl is main chemical component
• Desert Contamination: Salt in sand & deposits of insoluble material
• Industrial & Agricultural Contamination: Cement, soot and etc.

Corrosion

Page top

3. Flashover Mechanism

• Dry band formation near cap and pin by high density of leakage current
• Partial discharge at dry band
• Development into overall flashover

4. Influence of Contaminants

• NaCl shows the lowest withstand voltage among soluble material.
• Withstand voltage decreases with amount of non-soluble material, which retains moisture in the contamination layer.

5. Evaluation of Contamination Performance

• Clean fog method is recommended test, because it provides almost minimum envelope curve of test results on naturally contaminated insulators.
• Shed profile is designed by numerous contamination test results, including actual scale insulator string in High Voltage Laboratory

6. Anti-Contamination Design Procedures

Page top

7. Countermeasures against Contamination Problems

There are several countermeasures against contamination problems based on environmental condition, type of contaminants and cost.

A) Suspension (Disc) Insulators

(1) Increase leakage distance

For type Insulator

(2) To prevent contamination accumulation

For type Insulator

(3) To prevent dry band formation

Semiconducting glaze Insulator

B) Station Post & Hollow Insulators

(1) Increase leakage distance

(2) To prevent dry band formation

Semiconducting Glaze Insulators with various shed profile